Mature vascular smooth muscle cells (SMC) retain the ability to reversibly dedifferentiate and dramatically alter their phenotype in response to environmental cues. This plasticity allows for vascular repair and growth, but also contributes to cardiovascular pathologies including atherosclerosis, intimal hyperplasia, aneurysm, transplant arteriosclerosis, and others. Little is known about the epigenetic control of SMC phenotypic switching. We have recently identified TET2 as a novel master epigenetic regulator of SMC phenotype that promotes SMC differentiation and is downregulated in diseased vessels. TET2 promotes expression of key transcriptional drivers of SMC differentiation including myocardin and SRF while simultaneously inhibiting expression of KLF4, a transcription factor associated with dedifferentiation in SMC and pluripotency in stem cells. In addition to its known function of generating the epigenetic mark 5 hydroxymethylcytosine (5hmC), we have determined that TET2 also influences histone methylation, indicating that TET2 is involved in global chromatin remodeling in SMC. Others have shown association between TET2 and HDACs in hematopoietic cells. Our new preliminary data indicate a physical and functional association between TET2 and histone acetyltransferases (HATs). HATs acetylate histones in enhancer regions to promote cell type-specific gene expression. We have made the surprising observation that the HATs p300 and CBP, often considered to be interchangeable, have opposing roles in regulating SMC gene expression. We find that p300 is required to induce SMC differentiation in culture, while CBP is required for de-differentiation. Notably, these HATs also oppositely influence 5hmC at contractile promoters in SMC, and we detect a differentiation-dependent association between p300 and TET2. We hypothesize that p300 and CBP regulate distinct enhancers at contractile- and synthetic phenotype-specific genes, respectively, and are critical factors in SMC phenotypic switching. We further propose that TET2/p300 interactions may coordinately regulate chromatin conformation. The overall goal of this proposal is to identify the mechanisms by which p300, CBP, and TET coordinately regulate SMC phenotypic plasticity. We will employ state-of-the art molecular biology approaches, animal models, and advanced genomics techniques to address the central hypothesis that p300 and CBP regulate opposing programs of gene expression by acetylating distinct cis regulatory elements, and that HATs and TET2 work in concert to remodel chromatin during SMC phenotype modulation. Aim 1 will determine the mechanistic roles of p300 and CBP in SMC phenotypic modulation. Aim 2 will aim to define the opposing roles of p300 and CBP on vascular injury response in vivo. Aim 3 will determine how enhancers are regulated by p300, CBP, and TET2 using deletion approaches in vitro and in vivo. Collectively, these studies will lead to new understanding of SMC phenotypic modulation, which has potential for generating new preventive and therapeutic strategies for cardiovascular diseases.